Ultrasonic Cleaner for that size is pretty pricey. What kind of solution was used?

How about using gun cleaner solution like Hoppie's? Or, Non-corrosive degreaser?

It's an 8 gallon unit and you can pick one up for around $800. I use a 70/30 mix of pinesol (30%) and water (70%). It also heats the mixture up to 150-175 degrees F. Most shops will have one and won't charge much to clean some pistons. I did a few out of an old yamaha xs850 for a guy and charged him $30 to do 3 pistons.